1. Field of the Invention
The present invention relates to liquid crystal compositions exhibiting a chiral smectic C phase, and more particularly to liquid crystal compositions exhibiting the chiral smectic C phase and useful for ferroelectric liquid crystal display devices with high capacities and wide viewing angles.
2. Description of the Prior Art
Presently liquid crystal display devices predominantly utilize the nematic phase of liquid crystals, while active research has also been conducted in recent years on various display modes utilizing a smectic phase. Especially promising is ferroelectric liquid crystal display utilizing a chiral smectic C phase (hereinafter referred to merely as "ferroelectric liquid crystal display") because this mode of display is adapted to high-capacity display with wide viewing angles.
Unlike usual TN (twisted nematic) liquid crystal display, however, ferroelectric liquid crystal display, which utilizes the memory characteristics of the smectic C phase, requires a higher response speed for an increased display capacity. For example, when a drive method is used wherein one screen is rewritten at 1/60 sec with application of 4 pulses for rewriting one line, the response speed .tau. has the following relationship with the number of lines, L, that can be displayed at this speed. EQU 4.times..tau..times.L=1/60 sec
Thus, an exceedingly high response speed is required of the liquid crystals for use in high-capacity liquid crystal display devices.
To fulfill various requirements, therefore, liquid crystal compositions incorporating a plurality of compounds are conventionally used for ferroelectric liquid crystal display as is the case with nematic liquid crystal display, whereas compositions which are fully satisfactory in respect of the response speed still remain to be developed.
While the liquid crystal composition for ferroelectric liquid crystal display must be highly responsive as stated above, the other properties desirable for the composition include the following. First, the composition needs to exhibit the smectic C phase at around room temperature. Further to be satisfactory in the orientation of liquid crystals, the composition preferably exhibits IAC (isotropic-smectic A-smectic C) or INAC (isotropic-nematic-smectic A-smectic C) phase series.
From the foregoing viewpoint, we have carried out intensive research and consequently found that a chiral smectic liquid crystal composition having high responsibility and the desired properties described for use in ferroelectric liquid crystal display can be prepared by admixing a small amount of a compound represented by the formula (A) given below with a liquid crystal compound exhibiting the smectic C phase. The present invention has been accomplished based on this finding.